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This invention relates to color sequential video and multimedia projectors and more particularly to a prism-based optical engine that performs light beam integration, beam shaping, and input/output light separation.
Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. More recently, presentations using multimedia projection systems have become popular for conducting sales demonstrations, business meetings, and classroom instruction.
In a common operating mode, multimedia projection systems receive analog video signals from a personal computer (xe2x80x9cPCxe2x80x9d). The video signals may represent still, partial-, or full-motion display images of a type rendered by the PC. The analog video signals are typically converted in the projection system into digital video signals that control a digitally driven image-forming device, such as a liquid crystal display (xe2x80x9cLCDxe2x80x9d) or a digital micro mirror device (xe2x80x9cDMDxe2x80x9d).
It is becoming more important to provide a display system that is compact but that provides a high-quality image. Significant effort has been invested into developing projectors producing bright, high-quality, color images. However, it is difficult to obtain a suitable projected image, especially when using compact portable color projectors in a well-lighted room. For example, current display systems are heavy and bulky because of the number of required optical elements and the placement and spacing of the optical elements.
FIG. 1 shows such a system. An image projector 10 includes a high power lamp 12 positioned at the focus of an elliptical reflector 14 to produce a high intensity illumination beam characterized by a principal ray 16 that propagates through a rotating color wheel disk 18 of a color wheel assembly 20. Disk 18 includes at least three sectors, each tinted in a different one of three primary colors to provide a field sequential color image capability for image projector 10. The illumination beam propagates through an integrator tunnel 22 to create at its output end a uniform illumination pattern.
The illumination beam propagates from integrator tunnel 22 through lens elements 24 and 26 and is directed by a mirror 32 that is inclined so that the illumination beam propagates upwardly at a 45 degree angle relative to the plane of the supporting table for image projector 10. After reflection by mirror 32, principal ray 16 propagates through lens element 28 toward a prism assembly 40. Prism assembly 40 is composed of prism components 42 and 44 that are spaced apart by an interface 46.
An incident light beam derived from principal ray 16 propagates through prism component 42 and, by total internal reflection, reflects off of a surface at air space interface 46 to form a reflected incident light beam. The reflected incident beam propagates through prism component 42 to strike light valve 30. Light valve 30 reflects an imaging light beam propagating normal to the plane of light valve 30 through prism component 42 and, without total internal reflection, through interface 46 into prism 44 to exit through an exit face 60 of prism component 44. The imaging light beam that passes through exit face 60 is characterized by a principal ray 62 and propagates through a projection lens 64 to a projector screen (not shown) to display an image to a viewer.
As can be seen, this architecture employs many optical elements to integrate the light and to reflect, redirect, and transmit various polarized light or light rays depending on whether they propagate in a direction toward a display device. These optical elements add weight and bulk to the display system and are more costly to manufacture and more time consuming to assemble. Additionally, the arrangement of the components, such as, for example, the necessary upward inclination of prism assembly 40, dictates for a housing (not shown) a minimum height that is greater than desired.
What is needed, therefore, is a compact, light weight, low-profile multimedia projection system that achieves a bright, high-quality projected image at a relatively low cost.
An object of this invention is, therefore, to provide a multimedia display device having a simplified prism-based optics system.
Another object of the invention is to provide a multimedia projector in which the prism assembly is a totally integrated system that performs light integration, beam shaping, and input/output beam separation.
A further object of the invention is to provide a multimedia projector that eliminates the need for optical components to relay the image from the integrator onto a display device.
Still another object of the invention is to provide a multimedia projector that can be used with a transmissive or reflective LCD or a DMD.
Yet another object of this invention is to provide a multimedia projector that requires fewer parts, is lighter weight, more compact, less costly, and more easily assembled than prior projection systems.
A frame sequential color display projection system of this invention includes an arc lamp having a predetermined power rating for providing a source of polychromatic light that propagates through a color wheel that sequentially provides R, G, B, and optionally, W light colors during respective sequential time periods. A display controller is synchronized with the color wheel to generate color image data during the respective time periods. The light propagates through an integrated prism-based optical device that performs light integration, beam shaping, and input/output beam separation to create a uniform illumination pattern and to direct light toward or away from a display device.
In the preferred embodiment, the integrated optical device includes a light integrator tunnel with a first lens abutting one end of the light integrator tunnel. A prism is positioned in an abutting relationship at one side to the opposite end of the integrator tunnel, and a second lens abuts another side of the prism. Preferably, the individual elements are secured together using an index matching adhesive that matches the refractive index of the optical elements, which are typically made of glass so that together the integrator tunnel, prism, and lenses form a unitary element.
The integrated optical device is positioned within the projection system with one end adjacent to the color wheel and the opposite end closely adjacent to the display device. The close proximity of the integrated optical device to the display device eliminates the need for additional optical elements to reimage the light onto the display device. Additionally, placement of the integrated optical device adjacent the display device provides uniform, high intensity light from the color wheel to the display device.
In addition to integrating the incoming light from the lamp, the integrated optical device decreases the angular direction of the light as it propagates through the integrated optical device. This allows the use of an F1 reflector, which is a small reflector with a short working distance resulting in a smaller and more compact projection device. The second lens element reduces polarization losses associated with some light valves but may be eliminated depending on the type of light valve used.
The integrator tunnel may have a wedge or frustum shape that eliminates the need for the first lens because the wedge or frustum shape performs the function of reducing the incident angle of the incoming light. Depending on the type of light valve employed, it may not be necessary to use lenses. However, it may be necessary to use a lens between the prism and display device to reduce polarization losses associated with some light valves.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof that proceeds with reference to the accompanying drawings.